Applicant hereby claims foreign priority under 35 U.S.C. xc2xa7 119 from Swiss Patent Application No. 2002 1001/02 filed 12 Jun. 2002, the disclosure of which is herein incorporated by reference.
The present invention relates to a method of tracking a target and a target tracking system.
The present invention is particularly, but not exclusively, implemented in the context of tracking flying targets which are to be combated.
Typically, a search sensor and a tracking sensor are used for this purpose. The search sensor, which covers a search space, is particularly intended for the purpose of searching its search space for a target located therein and determining target information in this way, which describes at least the movement of the target and/or the track of the target in the past. The target information typically includes further data about the target, particularly about the type of target. In general, it is expedient to design the search sensor in such a way that it may be active using a large range and in a wide angular region, i.e., in a broad search space, and may provide detailed target information. Search sensors typically operate using relatively low search clock rates. Extrapolative flight path data is then established from the data determined by the search sensor, which describes the expected movement of the target in the future. This flight path data is essentially used for the purpose of performing a coarse alignment of the tracking sensor. The tracking sensor is frequently designed so that it covers a tracking space which is more restricted than the search space of the search sensor. After taking over the target from the search sensor, the tracking sensor must search for the target again in a starting phase of its activity before it may detect the target, align itself to the target, and track the target.
The main disadvantage of this typical method is that the target is not taken over by the tracking sensor without problems. The problems are particularly severe in this case if the tracking sensor has worse vision properties and/or a significantly smaller field of view and/or a different range than the search sensor. A further disadvantage is that the search clock rate of the sensor, which at least partially determines the method sequence, and which is used to provide the target aircraft data for the tracking sensor, is relatively low, but the search clock rate may not be increased at an acceptable cost.
A method and a system for a fire-control system of a manually aimable weapon are known from U.S. Pat. No. 5,379,676. In this case, a sensor system is provided, having a radar device and an electro-optical recognition system in the form of an FLIR camera. This method and this system are relatively complex in their construction, but the results achieved therewith are still not satisfactory.
It is therefore the object of the present invention,
to suggest an improved method of the type initially cited; and
to provide a target tracking system for performing this method, using which the disadvantages of the related art are avoided.
The novel method runs as follows: The search sensor searches its search space for a target, as in the typical method. In this case, the search space is searched at a first clock rate and/or search clock rate in multiple search passes. The search clock rate does not have to be precisely constant for this purpose. The search sensor determines an image sequence from each viewing angle, the time interval of the images of an image sequence being determined by the first clock rate and/or search clock rate. Digital images are also to be understood as images in this context. For rotating sensors, the first clock rate and/or search clock rate generally corresponds to the number of search sensor rotations per unit of time. If a target is located in the search space, the search sensor establishes target information at its search clock rate during multiple sequential search passes and/or search sensor rotations. The target information describes, possibly using interpolations, the track which the target has already flown through. The target information may also contain further details about the target, for example, information about the target type or results of a friend/foe query, through which targets detected are classified as objects to be combated, i.e., actual targets, or as friendly aircraft. With knowledge of the target information of multiple search passes, but possibly only using the target information relating to enemy targets, an expected flight path and/or flight path data, which describe the flight path the target is expected to take in the future, are provided through extrapolation. Instead of taking over the target directly, as in the typical method, searching for the target from the beginning once again at this time, and tracking it autonomously, in the novel method, the tracking sensor does not track the sensor autonomously, but externally controlled. The external control is performed on the basis of the flight path data provided to the tracking sensor at a second clock rate, which is higher than the first clock rate and/or search clock rate. During the transition phase, the externally controlled tracking sensor is aimed at the expected flight path, even if the target is in the tracking space, but may not be sensed by the tracking sensor. As soon as the target may be sensed, it is detected by the tracking sensor, through which the transition phase and/or the external control of the tracking sensor is ended. From now on, the tracking sensor is tracked on the target autonomously and/or tracks the target autonomously. During the transition phase, the target may not be directly sensed by the tracking sensor, but the tracking sensor nonetheless tracks the target in a way which may be referred to as xe2x80x9cblindxe2x80x9d, at least approximately in the scope of the possible precision, which is determined by extrapolation, among other things. Searching for the target again, this time by the tracking sensor, is not necessary. In the moment in which it may directly sense the target, the tracking sensor is already aimed at the target. In practice, a target point, which the tracking sensor is aimed at, and the target point surroundings are shown with the aid of a display unit (in the form of a monitor, for example), an arrangement in which the target point occupies the center of the monitor typically being selected. In the novel method, when the target may be sensed directly by the tracking sensor, it appears in direct proximity to the target point (or within a gate which is displayed on the monitor); the target would appear exactly around the target point if the actual flight path was coincident with the extrapolated flight path and no other uncompensated errors were noticeable. For transmission within the system of the data used in connection with the novel method, the target tracking system also has the typical suitable transmission means. In addition, it is also to be noted that the particular data is, of course, also updated continuously or in a clocked way, taking the particular newest target information into consideration.
The advantages achieved using the present invention are essentially as follows: an operator at the tracking sensor must neither perform manual search movements nor initiate automatic search movements as long as no target appears on the monitor of the tracking sensor; reasons that no target appears could be as follows: the target is not yet in the tracking space and/or is too small; the target is in the tracking space, but the view of the target is covered or not recognizable due to atmospheric absorption. At latest when the target reaches the tracking space, the tracking sensor acts, with the aid of the external control, as it would if it was able to detect the target, although it is xe2x80x9ctarget-blindxe2x80x9d; the tracking sensor may possibly also be aimed at the target and/or the suspected flight path before the target reaches the tracking space. In any case, the detection of the target is always ensured if the search sensor has found a target. The operator may therefore concentrate on waiting for the end of the transition phase, and thus the appearance of the target on the monitor, in order to subsequently optically/manually or automatically track the tracking sensor on the target. Even after long xe2x80x9cblindxe2x80x9d target tracking, the target, which may then be sensed directly by the tracking sensor, may be rapidly tracked and possibly rapidly combated, in any case, significantly more rapidly than with the typical use of the flight path data, which was provided only at the low first clock rate and/or search clock rate.
For flawless and efficient performance of the novel method, it is not necessary for the search sensor and the tracking sensor to have identical search characteristics or specific search characteristics tailored to one another. This has the advantage that different sensors, from different weapons systems, for example, are usable together by being coupled into an efficiently acting sensor composite, through which the value of each sensor for combating targets increases. This is especially advantageous because the tracking sensors are frequently components of already existing weapon systems, whose efficiency may be elevated by working together with search sensors.
In particular, the search sensor and the tracking sensor may have unequal ranges and/or cover unequal angular spaces, the search sensor generally having a larger range and usually also able to search a broader angular space.
In certain cases, it may be advantageous to provide a search sensor with search sensor units having multiple different capabilities; the search sensor units may, for example, be responsible for different partial search spaces which nonetheless overlap easily, or they may be responsible for the same search space but with different view and/or detection relationships; these include not only different conditions in the space between sensor and target, but also different properties of the target, which lead to different detection results.
Frequently, a radar sensor is used as a search sensor and an infrared sensor, preferably an FLIR sensor, or a TV camera or an optical line of sight is used as a tracking sensor, for example.
The tracking sensor is preferably implemented so that it is aimable at the target completely independently of the direct detectability of target by the sensor itself, possibly even if the target is not yet in the space which may be sensed by the tracking sensor.
The tracking means of the tracking sensor may be implemented for manual or automatic tracking of the tracking sensor. Tracking sensors which may be tracked both automatically and manually are advantageous, so that a malfunction of the automatic tracking system does not cause the malfunction of the entire tracking sensor.
The novel method is especially suitable in cases in which the tracking sensor is positioned spatially separate from the search sensor, but, of course, in a known relative position to the search sensor. To achieve more precise results, the relative position must be included in the calculations in this case. Frequently, but not necessarily, search sensors are fixed and tracking sensors are mobile. Search sensors may form components of complex fixed early warning systems, while tracking sensors may form components of fire control devices or weapon carriers of weapons systems, which are frequently not fixed.
The search sensor and/or the tracking sensor may be equipped with appropriate search means for establishing the particular relative positions.
Individual calculation units may form the calculation means necessary in connection with performing the method. Such calculation units may be assigned to both the search sensor and the tracking sensor. Generally, both the search sensor and the tracking sensor, and frequently also auxiliary systems such as weapons carriers, have specifically implemented calculation units.
In many cases, the target tracking system has only one search sensor, but more than one tracking sensor. If a further tracking sensor is in a different relative position to the search sensor than the first tracking sensor cited, further flight path data, which takes the different relative position of the further tracking sensor into consideration, is to be provided for the further tracking sensor.
Flight path data or further data essential to the method may be transmitted specifically to an auxiliary system with the aid of communication means. The auxiliary system may, for example, be a weapons carrier, particularly a gun or a rocket launcher. The weapon carrier may also be mobile. Weapon barrels of guns and/or the corresponding servos are frequently controlled with the aid of tracking sensors. In this context, the weapon carriers fire projectiles, also referred to as weapons, which are to hit the target, frequently in fragments. The data must take the relative position of the weapon carrier to the tracking sensor into consideration for this purpose, and a lead calculation must be performed for controlling the weapon barrel, which takes the flight behavior and/or the ballistics of the projectiles into consideration in particular.
In an especially advantageous embodiment, the search sensor may also be implemented so that it may establish target information of not just one, but rather multiple targets. The target information, which relates to different targets, is then analyzed with the aid of the calculation means, which has a specific intelligence for this purpose, and provided for different tracking sensors.
It is typical for the tracking sensors to have filter means, and it is a special advantage of the present invention that such filters may be preset taking the flight path data into consideration.
In practice it is unavoidable that the novel target tracking system is implemented so that time delays caused by the system arise when the novel method is implemented. In order to avoid errors caused by such time delays, it is advantageous to perform the calculations while taking the time delays into consideration, so that a compensation is performed to track the tracking sensor more precisely.